The development of new and more energy-efficient illumination devices is one of the important technical challenges which society faces. Common technologies which are more energy-efficient than traditional lighting solutions are often based on light-emitting diodes (LEDs). Currently, the reduced cost and improved performance of LEDs enable their use for general illumination. The small size of LEDs allows for easy integration of LEDs into building materials and furniture.
Combining these trends, the general illumination of an indoor space may be provided by a luminous ceiling, rather than by discrete fixtures in a dark ceiling. Such diffuse, large-area and low-brightness ceiling sources provide comfortable lighting with low glare and almost no shadows, while creating an aesthetic, clean ceiling without disturbing fixtures. The recent development of acoustic absorbing ceiling tiles with embedded lighting enables a full coverage of the ceiling with light without deteriorating the acoustics in the room.
Daylight through windows results in lighting that differs from indoor lighting in intensity, in color temperature, and directionality (shadows and contrast). Conventional indoor lighting systems may be equipped with photo-sensors, such that the increase in illumination level caused by daylight may be compensated by dimming down the artificial lighting. Unwanted gradients in illumination level are compensated by changing the dimming level as a function of the distance to the window, or by using a control loop to adjust the local illumination level to a certain predefined value. The controls may also be linked to blinds to regulate the amount of incoming daylight. An example of a prior art indoor lighting system with daylight controls can be found in U.S. Pat. No. 7,190,126, which also further describes an office lighting system with controls that regulate the light flux as function of the amount of daylight incident in a room.